The following discussion concerns mainly the processing of trouble of the atrial rhythm with such devices, including, for example, processing by "double chamber" devices that collect (sense) and deliver (stimulate) signals both in the atrium and the ventricle, and "single chamber" devices that collect and deliver signals only in the atrium.
The location for detecting cardiac arrhythmia troubles to be processed by the invention, as will be discussed below, is not, however, limited to troubles detected in the atrium, and the invention will be able to be equally applied, mutatis mutandis, to the processing of trouble of the ventricular rhythm, the cavity of the myocardium then being considered as the ventricle, instead of the atrium.
The term "trouble of the atrial rhythm" or TdRA is a generic term that covers various atrial arrhythmia (episodes of non physiological acceleration of the rhythm) such as tachycardia, fibrillation, flutter, etc. These troubles or TdRA are all characterized at the detection, by a rapid atrial rhythm.
When one detects a TdRA, that is to say essentially when the atrial rhythm exceeds an admissible (selected or allowable) level, the pacemaker switches to operation in a mode called "desynchronisation" or "atrio-ventricular dissociation". In this mode, the ventricle is stimulated independently of the detected atrial rhythm, since this excessive rhythm is considered to be pathological.
In a general manner, one has observed that patients presented less atrial arrhythmia when they were always stimulated. A simple solution would be always to stimulate the atrium or atria at a fixed rhythm much greater than the physiological rhythm, but it would be nevertheless dangerous, in the long run, to the clinical state of the patient.
U.S. Pat. No. 4,419,996 describes a device susceptible to function according to two different modes, namely a first normal mode, inhibited, suitable to process bradycardia-type arrhythmias, and a second mode, dissociated, under the command of a programmed external device, in a manner as to treat the tachycardia-type arrhythmias.
The switching from the first to the second mode is obtained by bringing a magnet in proximity to the device, which supposes that it is the patient, or a therapist, that decides and controls the passage from one mode to the other. The device operates therefore in an non-automatic manner, and according to a personal appreciation of the patient or the therapist.
WO-A-95 09661 describes a device allowing the asynchronous stimulation of the atrium, stimulation that is implemented according to the evolution of the sinus rhythm of the patient and the information provided by a sensor of the activity of the patient, so as to adapt the functioning to real physiological needs of the patient. This device presents, however, the disadvantage of necessitating a supplementary information source (the sensor of activity) that, in addition, is not always available, for example, when the patient is at rest.